In this project we studied the release of the endogeneous protein activator from rat brain membrane fraction by some putative neurotransmitters. Those neurotransmitters that activate adenylate cyclase released significant quantities of activator. There was a correlation between the activity of those agents as adenylate cyclase stimulators and the degree of activator release. Serotonin, which did not stimulate adenylate cyclase activity failed to show any activator release. Dopamine was most active in both adenylate cyclase activation and activator release using preparation from caudate nucleus. Norepinephrine was much more active when membrane fraction from cerebellum was used. The release of activator by the neurotransmitter was further used as a model to study the effect of some psychoactive drugs on this process. It was established that correlation exists between the clinical activity by those drugs and their potency to block activator release.